Use appropriate storage location + migrate events

[bsneed]

• Use applicationSupportDirectory for storage instead of documents/cache.
• Migrate any existing event batches.
• Added test to verify migration.

[codecov]

Codecov Report

❌ Patch coverage is 96.77419% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 70.91%. Comparing base (96380e2) to head (3701acc).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
Sources/Segment/Utilities/Utils.swift	96.77%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #399      +/-   ##
==========================================
+ Coverage   70.80%   70.91%   +0.11%     
==========================================
  Files          49       49              
  Lines        4894     4920      +26     
==========================================
+ Hits         3465     3489      +24     
- Misses       1429     1431       +2     

Files with missing lines	Coverage Δ
Sources/Segment/State.swift	97.35% <ø> (-0.02%)	⬇️
Sources/Segment/Utilities/Utils.swift	67.56% <96.77%> (+16.50%)	⬆️

... and 2 files with indirect coverage changes

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